We report on the preparation and characterization of two new air‐stable mononuclear molybdenum(VI) complexes, termed MoVIO2(OPNO)2 (1) and MoVIO2(SPNO)2 (2). The potential of these complexes to act ...as functional mimics of molybdoenzymes from the DMSO reductase family was investigated. Initial catalytic studies suggest that 2 (but not 1) catalyzes the reduction of a sulfoxide into the thioether derivative. Studying the catalytic intermediates by UV/Vis spectroscopy, NMR spectroscopy, and DFT indicates that the active species (SPNO)2OMoV–O–MoVO(SPNO)2 (4), a dinuclear molybdenum(V) dimer with one µ‐oxo bridge, is formed upon successive reduction of the (SPNO)– ligands and the molybdenum(VI) ion.
Two new complexes of bis‐oxo‐molybdenum have been prepared and investigated in oxygen transfer reactions. Mo(OPNO)2O2 is inactive in this reaction under our conditions. In contrast, Mo(SPNO)2O2 can act as a (pre)catalyst in this reaction. On the basis of the combined theoretical and spectroscopic results, a mechanism is proposed involving a µ‐oxo MoV dimer.
In this report, we investigate on a biomimetic model of a H-bonded TyrZ/His190 pair covalently attached to a porphyrin sensitizer. Laser flash photolysis in presence of an external electron acceptor ...reveals the need of water molecules to unlock the light-induced oxidation of the phenol through an intramolecular pathway. Kinetics monitoring encompasses two fast phases with distinct spectral properties. The first phase is related to one-electron transfer from the phenol to the porphyrin radical cation coupled with a domino two-proton transfer leading to the ejection of a proton from the imidazole-phenol pair. The second phase concerns the convoy of the released proton to the porphyrin N4 coordinating cavity. Importantly, our study provides an unprecedented example of light induced electron transfer process in a TyrZ/His190 model of Photosystem II, evidencing the movement of both the phenol and imidazole protons along an isoenergetic pathway.
Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n-butyl lithium afforded the corresponding derivatives (1-aryl-1H-imidazol-2-yl)lithium (1a, Ar = Mes; 1b, ...Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of Ir(cod)(μ-Cl)2 yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex Ir(cod){μ-C3H2N2(Mes)-κC2,κN3}2 (3), 3H-H, a head-to-head (H-H) isomer of CS symmetry, and 3H-T, the thermodynamically preferred head-to-tail (H-T) isomer of C2 symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3H-H and 3H-T afforded the tetracarbonyl complexes Ir(CO)2{μ-C3H2N2(Mes)-κC2,κN3}24H-H and 4H-T, respectively. The reaction with PMe3, which gave only one complex, Ir(CO)(PMe3){μ-C3H2N2(Mes)-κC2,κN3}2 (5), demonstrates that the isomerization of the central core Irμ-C3H2N2(Mes)-κC2,κN32Ir from H-H to H-T on going from 4H-H to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal-metal bonded d(7)-d(7) complex Ir2(CO)2(PMe3)2(Me)I{μ-C3H2N2(Mes)-κC2,κN3}2 (6). The blue Ir(C2H4)2{μ-C3H2N2(Mes)-κC2,κN3}2 (7) and purple Rh(C2H4)2{μ-C3H2N2(Dipp)-κC2,κN3}2 (9) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3H-T, 4H-T and 5, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3H-T undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(i)/Ir(ii) system. The energy of the intervalence band for the orange dirhodium complex Rh(cod){μ-C3H2N2(Mes)-κC2,κN3}2 (8) is shifted toward lower energies in comparison with 3H-T, reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(i)/Ir(ii) and Rh(i)/Rh(ii) systems. The molecular structures of 3H-H, 3H-T, 8 and 9 have been determined by X-ray diffraction.
Electrocrystallization of
ortho
-dimethyltetrathiafulvalene (
o
-DMTTF) in the presence of a nitrite (NO
2
−
) anion affords a 2 : 1 phase, namely (
o
-DMTTF)
2
NO
2
, the first example of an ...isolated cation radical salt with NO
2
−
. The
o
-DMTTF molecule organizes into strongly dimerized stacks that adopt a rare chessboard organization, associated with a strongly 1D structure. As a consequence of dimerization, the salt exhibits a semiconducting behavior (
σ
RT
= 5 S cm
−1
,
E
act
= 0.1 eV). The bent NO
2
−
anion is disordered on the inversion center but does not exhibit any anion-ordering transition. Combined SQUID magnetometry and electron paramagnetic resonance (EPR) experiments demonstrate the appearance of a spin-Peierls transition with
T
SP
= 70 K. The temperature dependence of the spin gap and associated dimerization parameter
δ
across the spin-Peierls transition have been determined. The low-temperature narrow EPR line observed below
T
SP
is attributable to intrinsic magnetic defects localized on the
o
-DMTTF molecules themselves. The broadening of the EPR line at higher magnetic fields is associated with the disordered NO
2
−
anions surrounding these magnetic defects, contributing to the inhomogeneity of their
g
factor.
The first nitrite salt of a tetrathiafulvalene derivative exhibits a rare chessboard-like organization of the conducting stacks, with a spin-Peierls transition at 70 K.
Kupfer oder Nickel? Der gezeigte CuII‐Salen‐Komplex, ein Modell des aktiven Zentrums der Galactose‐Oxidase (GO), liegt im Festkörper als lokalisiertes Radikal vor, wie an der chinoiden Verteilung der ...Bindungslängen in einem der Ringe zu erkennen ist. Die Struktur des radikalischen Liganden hängt nicht vom Metall ab, die Zusammensetzung des SOMO dagegen schon. Dies könnte die viel geringere Reaktivität des Ni‐Komplexes erklären, ebenso wie die Tatsache, dass natürliche GO ein CuII‐Zentrum bevorzugt.
The diimino-diphenolato neutral square-planar Ni(
ii
) complex, NiL
2
, is readily oxidised with 2 equiv. of AgSbF
6
, to produce an unprecedented octahedral Ni(
ii
) tris(phenoxyl) radical complex, ...Ni(L&z.rad;)
3
SbF
6
2
. This study reveals, for the first time, the X-ray structure of a metal-tri-phenoxyl radical complex.
The diimino-diphenolato neutral square-planar Ni(
ii
) complex, NiL
2
, is readily oxidised with 2 equiv. of AgSbF
6
, to produce an unprecedented octahedral Ni(
ii
) tris(phenoxyl) radical complex, Ni(L&z.rad;)
3
SbF
6
2
. This study reveals, for the first time, the X-ray structure of a metal-tri-phenoxyl radical complex.
The syntheses and single-crystal X-ray structures of the mononuclear complexes Cu(bmet)(ClO4)2·H2O, Cu(bmet)Br2·2MeCN, and Zn(bmet)(ClO4)2·H2O (bmet = ...N,N′-bis(2,2′-bipyridin-6-ylmethyl)ethane-1,2-diamine) are described. All three complexes feature a central metal ion bound to all six N atoms of the bmet ligand, which displays a meridional-facial-facial-meridional (mffm) configuration. The three complexes show one N–M–N axis to be significantly shorter than the others in agreement with an apparent compressed octahedral geometry. The X-ray structures of a single crystal of Cu(bmet)(ClO4)2·0.375H2O resolved from data recorded at different temperatures display no remarkable structural modifications. However, they all display both as a powder and, in solution, an axial g 1 > g2 ≳ g 3 > g e electron paramagnetic resonance (EPR) pattern at low temperature, which is indicative of tetragonally elongated octahedra, while at room temperature the Q-band EPR spectra display a more rhombic g 1 ≳ g 2 > g3 > g e pattern. The fully density functional theory optimized structure of the CuII complexes displays significant structural modifications only along one Nimine–M–Namine axis resulting in an elongated octahedral structure. Furthermore, the EPR parameters predicted from this structure are comparable to those determined experimentally from the axial EPR signal recorded at low temperature, consistent with the unpaired electron residing mainly in the {3d x 2 –y 2 } orbital. The structural and electronic properties of Cu(bmet)2+ are different from those in other previously described dynamic Jahn–Teller systems. We propose that these data can be rationalized by a dynamic Jahn–Teller effect perturbed by the strain of the hexadentate bmet ligand.
Two new heterobimetallic LNiO
2
Cu(RPY2)
+
(RPY2 =
N
-substituted bis 2-pyridyl(ethylamine) ligands with R = indane,
3a
or R = Me,
3b
) complexes have been spectroscopically trapped at low ...temperatures. They were prepared by reacting the mononuclear
side-on
LNi
II
superoxo precursor bearing a β-diketiminate ligand (L = HC-(CMeNC
6
H
3
(iPr)
2
)
2
) with the Cu(
i
) complexes. In contrast to the oxo groups in known high-valent M
2
(μ-O)
2
n
+
(M = Fe, Co, Ni, Cu) cores that display electrophilic reactivities,
3a
and
3b
display rather nucleophilic oxo cores active in aldehyde deformylation reactions. However, the spectroscopic and reactivity properties of
3a
/
3b
are found to be distinct relative to that of the previously reported LNiO
2
Cu(MeAN)
+
complex containing a more basic (nucleophilic)
N
,
N
,
N
′,
N
′,
N
′-pentamethyl-dipropylenetriamine (MeAN) ligand at the copper centre. The geometry and electronic properties of the copper ligands affect the electron density of the oxygen atoms of the heterodinuclear {Ni(μ-O)
2
} core and
3a
/
3b
undergo slower nucleophilic and faster electrophilic reactions than the previously reported LNiO
2
Cu(MeAN)
+
intermediate. The present study therefore demonstrates the tuning of the electrophilicity/nucleophilicity of the oxygen atoms of the heterobimetallic Ni(μ-O)
2
Cu
2+
cores by controlling the electron donation from the ancillary ligands, and underlines the significance of subtle electronic changes in the physical and chemical properties of the biologically relevant heterobimetallic metal-dioxygen intermediates.
Two new heterobimetallic LNiO
2
Cu(RPY2)
+
(RPY2 =
N
-substituted bis 2-pyridyl(ethylamine) ligands with R = indane,
3a
or R = Me,
3b
) complexes have been spectroscopically trapped at low temperatures.
The one-electron oxidation of the dianionic diamido-diphenoxo Ni(
ii
) complexes involving H-bonding (
1
2−
), or not (
2
2−
), yields the corresponding Ni(
iii
) species; the formation, stability ...and electronic structures of which are affected by the H-bonding interactions.
The one-electron oxidation of the dianionic diamido-diphenoxo Ni(
ii
) complexes involving H-bonding, or not, yields the corresponding Ni(
iii
) species, the formation, stability and electronic structures of which are affected by the H-bonding interactions.
Three neutral palladium(II) complexes Pd(Ln)2 (n = 1,2,3) containing benzotriazole‐phenolate ligands HL1 = 2‐(2H‐benzotriazol‐2‐yl)‐6‐dodecyl‐4‐methylphenol; HL2 = ...2‐(2H‐benzotriazol‐2‐yl)‐4,6‐di‐tert‐pentylphenol; HL3 = 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐bis(1‐methyl‐1‐phenylethyl)phenol were synthesized and characterized by several spectroscopic methods (1H, 13C NMR, UV‐Visible), ESI mass spectrometry and single‐crystal X‐ray diffraction. The geometry around the palladium(II) centre for each complex is described as distorted square planar. The complexes were tested as potential catalysts for electrochemical proton reduction in DMF using trifluoroacetic acid (TFA). Gas analysis under electrocatalytic conditions at a boron‐doped diamond working electrode confirmed the hydrogen production. After performing similar gas analysis experiments using a working mercury pool electrode, no hydrogen was detected which supports the concept that the active species of the catalytic process are palladium particles formed on the surface of the working electrode. The palladium(II) benzotriazolyl phenolate complexes facilitate the formation of particles for electrocatalytic hydrogen production. Furthermore, the palladium(II) complexes PdL2 and PdL3 were able to catalyse microwave‐assisted Heck and Sonogashira C–C coupling reactions.
Neutral lipophilic palladium complexes based on benzotriazole‐phenolate ligands can operate as C–C bond coupling catalysts (e.g., Heck, Sonogashira). Alternatively, upon electroreduction in DMF containing TFA, they form palladium particles which can produce hydrogen gas by proton reduction.
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